Logic circuit system and method of changing operating voltage of a programmable logic circuit

ABSTRACT

A logic circuit system with power consumption that is reduced by automatically varying the clock frequency and operating voltage according to processing capability imposed on programmable logic circuits. The programmable logic circuits are capable of achieving plural circuit functions dynamically and can change realized circuit functions during operation. In addition, the system has a voltage supply portion for supplying a voltage to the programmable logic circuits, a clock signal supply portion for supplying a clock signal to the programmable logic circuits, a change control portion for changing the circuit functions realized by the programmable logic circuits to any one of the circuit functions, an operation time measuring portion for measuring the operation times of the programmable logic circuits to perform processing to achieve the circuit functions, respectively, and a clock-and-voltage determination portion for determining the frequency of the clock signal and the voltage, using the operation times.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of Ser. No. 10/960,707,filed Oct. 8, 2004, which is based upon and claims the benefit ofpriority from Japanese Patent Applications No. 2003-349430, filed onOct. 8, 2003, and No. 2004-228919, filed on Aug. 5, 2004, the entirecontents of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a logic circuit system utilizingprogrammable logic circuits that can reconfigure their circuitconfiguration and change their circuit functions during operation.

2. Description of the Related Art

Where a circuit performing processing consisting of plural process stepsis made up of one integrated circuit, the processing capability of someportions of the integrated circuit are superfluous. Correspondingly,excess electric power is consumed, because the operating speed of thewhole integrated circuit is set to be capable of performing theprocessing of the process step that requires the highest processingcapability in spite of the fact that there are process steps requiringonly low processing capability.

An effective technique of reducing the power consumption of anintegrated circuit is to lower the operating voltage and the frequencyof the clock signal (i.e., clock frequency). However, where theoperating voltage is lowered, the upper limit of the operable clockfrequency is reduced. Where the clock frequency is lowered, theprocessing capability is reduced.

In recent years, programmable logic circuits capable of changing theircircuit functions during operation have been proposed. Such aprogrammable logic circuit can change the circuit configuration of thewhole or part of the circuit during operation of the circuit.Programmable logic circuits include FPGAs (field programmable gatearrays) capable of changing their logic configurations at high speed andDPGAs (dynamically programmable gate arrays). These arrays arehereinafter referred to simply as “programmable logic circuits”.

Conventionally, a technique in which unit circuits for executingprocessing steps corresponding to plural process steps, respectively,are configured on a programmable logic circuit in a time-shared mannerto process all the process steps has been proposed in Japanese PatentApplication (KOKAI) No. 2001-202236.

With the aforementioned technique for operating a programmable logiccircuit in a time-shared manner, a surplus of processing capability canbe reduced by operating unit circuits corresponding to process stepsrequiring high processing capability for long periods and by operatingunit circuits corresponding to process steps requiring only lowprocessing capability for short periods.

With this technique, however, it is necessary to appropriately set theproportions of the operating times of the unit circuits in advance. Thatis, it is not assumed that the technique copes with a case where theprocessing capabilities respectively imposed on the unit circuits varydynamically.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a logic circuit system capable ofreducing power consumption by automatically varying clock frequency andoperating voltage according to processing capabilities imposed on aprogrammable logic circuit.

According to one aspect of the present invention, there is provided alogic circuit system comprising a programmable logic circuit having acircuit configuration that is reconfigurable during operation, a circuitconfiguration information supplier configured to supply circuitconfiguration information about plural unit circuits to saidprogrammable logic circuit a change controller configured to change thecircuit configuration of said programmable logic circuit to any one ofsaid plural unit circuits an operation time measurer configured tomeasure operation times of said plural unit circuits on saidprogrammable logic circuit, and a clock-and-voltage supplier configuredto obtain both a frequency using said operation times and a voltagevalue using said operation times, and supply the clock signal having thefrequency and the voltage having the voltage value to said programmablelogic circuit.

According to another aspect of the invention, there is provided a methodof changing an operating voltage of a programmable logic circuit havinga circuit configuration that is reconfigurable during operation whenplural unit circuits are operated in a time-sharing manner on saidprogrammable logic circuit using each of circuit configuration datacorresponding to each of the plural unit circuits, said methodcomprising measuring operation times for each of said plural unitcircuits, calculating a new frequency of a clock signal supplied to saidprogrammable logic circuit, using said operation times, finding a newoperating voltage necessary to operate said programmable logic circuitat said frequency and changing the operating voltage and the clocksignal supplied to said programmable logic circuit to the new operatingvoltage and the new frequency.

It is to be understood that both the foregoing general description ofthe invention and the following detailed description are exemplary, butare not restrictive, of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention will become moreapparent from the following detailed description read in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a block diagram of a logic circuit system according to thefirst embodiment;

FIG. 2 is a block diagram of one example of a programmable logic circuitused in the first embodiment;

FIG. 3 is a high-level block diagram illustrating a logic circuit systemaccording to the first embodiment;

FIG. 4 is a flow chart of a process for finding a clock frequency andoperating voltage of the first embodiment;

FIG. 5 is a block diagram of a logic circuit system according to thesecond embodiment;

FIG. 6 is a diagram showing a summary of assignment adjustment of unitcircuits;

FIG. 7 is a block diagram of a control portion according to the secondembodiment;

FIG. 8 is a flow chart of a process for finding a clock frequency andoperating voltage of the second embodiment;

FIG. 9 is a flow chart of a process for finding a clock frequency andoperating voltage of the third embodiment;

FIG. 10 is a flow chart of a process for finding a clock frequency andoperating voltage of the forth embodiment;

FIG. 11 is a high-level block diagram illustrating an example of theoperations of the logic circuit system of respective embodiments of thepresent invention;

FIG. 12 is a high-level block diagram illustrating another example ofthe operations of the logic circuit system of respective embodiments ofthe present invention;

FIG. 13 is a high-level block diagram illustrating another example ofthe operations of the logic circuit system of respective embodiments ofthe present invention; and

FIG. 14 is a high-level block diagram illustrating another example ofthe operations of the logic circuit system of respective embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In each embodiment of the present invention, a programmable logiccircuit capable of altering achieved circuit functions during operationis used. This programmable logic circuit can change the achieved circuitfunctions by reconfiguring the configuration of the whole or part of thecircuit during operation. Examples include a FPGA (field programmablegate array) and a DPGA (dynamically programmable gate array) designed tobe capable of quickly implementing reconfiguration of the circuitconfiguration. These arrays are hereinafter referred to simply asprogrammable logic circuits (PLC).

FIG. 2 is a block diagram of a part of the structure of a programmablelogic circuit. This logic circuit has plural unit blocks 200 (one shown)and an inter-block connection portion 210 for controlling flow ofinformation between the unit blocks 200. The unit blocks 200 deliverresults of logical calculations using input information.

Each unit block 200 of the programmable logic circuit has a look-uptable (LUT) 201 performing logical calculations on input data based ongiven information (hereinafter often referred to as “circuitinformation”) about the circuit configuration and a D-flip-flop 202 forsynchronizing the output when the results of the calculations performedby the LUT 201 are output to the next stage of unit block 200 via theinter-block connection portion 210. Each unit block 200 has a RAM(Random Access Memory) 203 for storing plural pieces of circuitinformation and a switching portion 204 for switching the circuitinformation supplied to the LUT 201. Each unit block 200 has a RAM 205and a switching portion 206. The RAM 205 saves the status informationabout the D-flip-flop 202 when the circuit information supplied to theLUT 201 is switched. The switching portion 206 switches the statusinformation about the D-flip-flop 202. The switching portion 206 storesthe status information regarding the D-flip-flop 202 into the RAM 205and restores the status information stored in the RAM 205 to theD-flip-flop 202.

The inter-block connection portion 210 has a connection portion 211 forcontrolling the flow of information between the unit blocks 200according to given circuit information, a RAM 212 for storing pluralpieces of circuit information, and a switching portion 213 for switchingthe circuit information supplied to the connection portion 211.

Outputs from the plural unit blocks 200 are entered into the LUT 201 ofone unit block 200. The LUT 201 performs logical calculations using theinput data. The LUT 201 delivers the results of the calculations to theconnection portion 211 via the D-flip-flop 202. The connection portion211 delivers the results of the logical calculations to one or more unitblocks 200 specified by the circuit information.

The programmable logic circuit defines the contents of logicalcalculations performed by each unit block 200 according to circuitinformation supplied externally. The programmable logic circuit achievesa complex circuit by combining the unit blocks 200. The circuit achievedby the programmable logic circuit according to the circuit informationis hereinafter referred to as the “unit circuit”. The programmable logiccircuit achieves the unit circuit according to circuit informationsupplied from the outside. When another circuit information is supplied,the programmable logic circuit achieves another unit circuit accordingto the other circuit information.

A procedure of reconfiguring the circuit configuration during operationof the programmable logic circuit is hereinafter described. It isassumed that the reconfiguration is controlled by a control portion (notshown). Information about a circuit operated after switching includescircuit information 203-2, status information 205-2, and circuitinformation 212-2.

(A) The control portion supplies information about the circuit to beoperated next from the outside to the RAMs 203, 205, and 212. Thecontrol portion supplies circuit information 203-2 to the RAM 203. Thecontrol portion supplies status information 205-2 to the RAM 205. Thecontrol portion supplies the circuit information 212-2 to the RAM 212.

(B) The control portion stops the supply of the clock signal to theprogrammable logic circuit to stop the processing of the programmablelogic circuit.

(C-1) The control portion sends a control signal to the switchingportion 206. The switching portion 206 saves the status information205-1 held in the D-flip-flop 202 to the RAM 205.

(C-2) The control portion sends a control signal to the switchingportion 204. The switching portion 204 copies the circuit information203-2 stored in the RAM 203 into the LUT 201.

(C-3) The control portion sends a control signal to the switchingportion 213. The switching portion 213 supplies the circuit information212-2 stored in the RAM 212 to the connection portion 211.

(D) The control portion sends a control signal to the switching portion206. The switching portion 206 restores the status information 205-2stored in the RAM 205 onto the D-flip-flop 202.

(E) The control portion resumes the supply of the clock signal.

Reconfiguration of the circuit configuration of the programmable logiccircuit is carried out in the procedure described so far. The processing(A) above can be omitted where the RAMs 203, 205, and 212 already holdthe circuit information 203-2, status information 205-2, and circuitinformation 212-2.

The programmable logic circuit can quickly reconfigure the circuitconfiguration owing to a feature of the RAMs 203 and 205. In variousembodiments of the invention, the RAMs 203 and 205 are mounted. TheseRAMs 203 are not essential. Reconfiguration can also be accomplished bysending and receiving circuit information and status information at highspeed from outside the programmable logic circuit.

In FIG. 2, the number of kinds of information stored in the RAMs 203 and205 is two, i.e., circuit information and status information. More kindsof information may be stored. The number of kinds of information thatcan be stored in the RAMs 203 and 205 may be determined according to thespeeds at which the circuit information and status information are sentand received from the outside.

FIG. 3 schematically shows the functions of the logic circuit systems ofthe various embodiments of the invention. FIG. 3 shows an example ofcircuit that produces a final output through four processing steps A, B,C, and D when an input is made.

If such a circuit is accomplished by a combination of dedicatedcircuits, the following configuration is conceivable, for example. Adedicated circuit A for performing the processing step A, a dedicatedcircuit B for performing the processing step B, a dedicated circuit Cfor performing the processing step C, and a dedicated circuit D forperforming the processing step D are used. The outputs and inputs of thededicated circuits are connected via FIFOs 321, 322, and 323 to absorbthe differences in processing performance between the dedicated circuitsand in input/output data rate. Another FIFO 320 is mounted on the inputside of the dedicated circuit A. A further FIFO 324 is mounted on theoutput side of the dedicated circuit D.

Input data is supplied to FIFO 320. The input data is processed by thededicated circuits A, B, C, and D. Final output is obtained via the FIFO324.

The logic circuit system of each embodiment of the invention uses aprogrammable logic circuit instead of preparing four dedicated circuits.The four dedicated circuits are treated as unit circuits. Circuitinformation for realizing the unit circuits by the programmable logiccircuit is used. The logic circuit system reconfigures the circuitconfiguration during operation by supplying circuit information abouteach unit circuit to the programmable logic circuit. The programmablelogic circuit operates while dynamically switching the functions of theunit circuits (hereinafter may be referred to simply as “circuitfunctions”). That is, the four unit circuits share the programmablelogic circuit in a time-sharing manner. This produces the same effect asproduced when four dedicated circuits are physically prepared. Thus, thegeneral-purpose logic circuit system using programmable logic circuits300 produces the same effect as produced by the dedicated circuit 310.The outputs and inputs of the unit circuits are connected via the FIFOs320, 321, 322, 323, and 324.

The “unit circuit A realized by the programmable logic circuit (PLC)301” indicates the programmable logic circuit in the state in which thecircuit information A is supplied and the circuit is acting as the unitcircuit A. The “realization of the unit circuit A by means of theprogrammable logic circuit” is to realize the circuit functions of theunit circuit A by supplying the circuit information A to theprogrammable logic circuit.

Each of the four dedicated circuits is herein treated as a unit circuit.The present invention is not limited to this scheme. For example, acircuit obtained by dividing a dedicated circuit or a circuit obtainedby combining plural dedicated circuits may be treated as a single unitcircuit. The contents of each unit circuit may be determined accordingto the scale of the circuit of the dedicated circuit, the circuit scaleof the programmable logic circuit, the properties of the processing ofthe process steps, or the flow through the whole processing.

The control portion 302 controls switching of the circuit functions. Thecontrol portion 302 also causes the FIFO selecting portion 305 to selectan appropriate FIFO according to the circuit realized by theprogrammable logic circuit 301.

FIGS. 11, 12, 13, and 14 show the manner in which the programmable logiccircuit 301 operates while switching the circuit functions from instantto instant.

FIG. 11 shows the operation when the circuit information A is suppliedto the programmable logic circuit 301. In FIG. 11, the circuitinformation A is supplied to the programmable logic circuit 301 and sothe programmable logic circuit 301 functions as circuit A that performsthe processing of step A. The FIFO selecting portion 305 connects theFIFO 320 to the input side of the programmable logic circuit 301 and theFIFO 321 to the output side of the programmable logic circuit 301.

FIG. 12 shows the operation when the circuit information B is suppliedto the programmable logic circuit 301. In FIG. 12, the circuitinformation B is supplied to the logic programmable circuit 301 and sothe programmable logic circuit 301 functions as the circuit B thatperforms the processing of step B. Furthermore, the FIFO selectingportion 305 connects the FIFO 321 to the input and output sides of theprogrammable logic circuit 301 and the FIFO 322 to the output side ofthe programmable logic circuit 301.

FIG. 13 shows the operation when the circuit information C is suppliedto the programmable logic circuit 301. In FIG. 13, the circuitinformation C is supplied to the programmable logic circuit 301 and theprogrammable logic circuit 301 functions as circuit C that performs theprocessing of step C. The FIFO selecting portion 305 connects the FIFO322 to the input side of the programmable logic circuit 301 and the FIFO323 to the input and output side of the programmable logic circuit 301.

FIG. 14 shows the operation when the circuit information C is suppliedto the programmable logic circuit 301. In FIG. 14, circuit information Dis supplied to the programmable logic circuit 301 and the programmablelogic circuit 301 functions as circuit D that performs the processing ofstep D. The FIFO selecting portion 305 connects the FIFO 323 to theinput side of the programmable logic circuit 301 and the FIFO 324 to theinput and output side of the programmable logic circuit 301.

The logic circuit system of each embodiment of the present invention hasan operation time measuring portion 303 for measuring the operation timeof each unit circuit. The measuring portion 303 measures actualoperation times of n unit circuits. In the description provided below,the time for which each unit circuit has actually operated is a timeinterval from the instant when circuit information about the unitcircuit is supplied to the LUTs of the programmable logic circuit to theinstant when the supply of the clock signal is stopped to realize adifferent unit circuit.

The control portion 302 determines the timing of a reconfiguration ofthe programmable logic circuit. The control portion 302 monitors each ofthe amount of data stored in each of (n+1) FIFOs. The control portion302 determines the timing of a reconfiguration of the programmable logiccircuit according to each of the amount of data. That is, the controlportion 302 schedules the operations of the unit circuits.

Furthermore, the control portion 302 estimates the processing capabilityrequired by the programmable logic circuit, using the operation times ofthe unit circuits. The control portion 302 finds the frequency of theclock signal and operating voltage necessary to realize the estimatedprocessing capability. The control portion 302 then controls theclock-and-voltage supply portion 304, thus modifying the frequency ofthe clock signal supplied to the programmable logic circuit andoperating voltage.

For example, the control portion 302 estimates the processing capabilityusing the sum of the operation times of the unit circuits, the ratios ofthe operation times of the unit circuits, and the distribution of theoperation times of the unit circuits. Where there are pluralprogrammable logic circuits, the control portion 302 estimates theprocessing capability, also using the sum of the operation times, theratios of the operation times, and the distribution of the operationtimes for each individual programmable logic circuit.

First Exemplary Embodiment of a Logic Circuit System

FIG. 1 shows a logic circuit system using a programmable logic circuitaccording to a first exemplary embodiment of the present invention. Thelogic circuit system of the present exemplary embodiment has aprogrammable logic circuit 101 including an assemblage of the unitblocks 200 of FIG. 2, a circuit information supply portion 102 forsupplying circuit information from the outside to the programmable logiccircuit 101, and a circuit information storage portion 103 for storingthe circuit information.

The logic circuit system of the present exemplary embodiment has FIFOs106 connecting the unit circuits realized by the programmable logiccircuits 101, an input FIFO selecting portion 104 for selecting circuitswhich are connected with the input sides of the unit circuits realizedby the programmable logic circuit 101 from the FIFOs 106, and an outputFIFO selecting portion 105 for selecting circuits which are connectedwith the output sides of the unit circuits realized by the programmablelogic circuit 101 from the FIFOs 106.

The logic circuit system of the present embodiment has a statusinformation management portion 108 for managing status information aboutthe programmable logic circuit 101, a status information storage portion109 for storing the status information, an operation time measuringportion 110 for measuring the operation time of each unit circuit, and aclock-and-voltage supply portion 111 for supplying a clock signal and avoltage necessary for operation to the programmable logic circuit.

The programmable logic circuit 101 performs data processing whileswitching the functions of the N unit circuits from time to time. Theunit circuits realized by the programmable logic circuit 101 read outdata necessary for the processing from the FIFOs 106 via the input FIFOselecting portion 104. The unit circuits write data obtained as a resultof the processing into the FIFOs 106 via the FIFO selecting portion 105.The programmable logic circuit 101 modifies the circuit configuration inresponse to a control signal from the control portion 107. For purposesof explanation, the following premises are made in the present example,however the present invention is not limited by these premises:

(A1) All the unit circuits of the present exemplary embodiments areconnected in series.

(A2) Each unit circuit of the present exemplary embodiment has one inputand one output.

(A3) The whole logic circuit system of the present exemplary embodimenthas one input and one output.

The circuit information supply portion 102 reads circuit information ofthe unit circuit specified by the control portion 107 from the circuitinformation storage portion 103. The circuit information supply portion102 supplies the circuit information read out to the programmable logiccircuit 101.

The circuit information storage portion 103 stores circuit information103-1, 103-2, . . . , 103-N. Each of the circuit information 103-1,103-2, . . . , 103-N corresponds to each of the N unit circuits. Theunit circuit realized by the programmable logic circuit 101 usingcircuit information 103-k is hereinafter referred to as the unit circuit103-k. For purposes of explanation, the following premises are added inthe present example, however the present invention is not limited bythese premises:

(A4) In the present exemplary embodiment, the unit circuit 103-kperforms the processing of the k-th (k=1, 2, . . . , N) step of the dataprocessing performed by the logic circuit system of the presentembodiment. The unit circuit 103-N is the closest of the unit circuitsto the output side of the whole logic circuit system.

The FIFOs 106 include (N−1) FIFOs (FIFOs 106-1, 106-2, . . . ,106-(N−1)) connecting the N unit circuits. A FIFO 106-a is on the inputside of the whole circuit. A FIFO 106-b is on the output side of thewhole circuit. For purposes of explanation, the following premises areadded in the present example, however, the present invention is notlimited by these premises:

(A5) The FIFO connected with the output side of the unit circuit 103-kis the FIFO 106-k.

(A6) The FIFO connected with the input side of the unit circuit103-(k+1) is the FIFO 106-k.

(A7) Each of the FIFOs has the same capacity.

The FIFOs 106 are not limited to a first-in, first-out dedicated memory.A memory such as a DRAM configured or controlled to enable first-infirst-out operation is also applicable.

The input FIFO selecting portion 104 selects the input FIFO to beconnected with the unit circuit specified by the control portion 107 outof the FIFOs 106. Data is supplied from the selected input FIFO to thespecified unit circuit configured on the programmable logic circuit 101.

The output FIFO selecting portion 105 selects the output FIFO to beconnected with the unit circuit specified by the control portion 107 outof the FIFOs 106. The data that is output from the specified unitcircuit configured on the programmable logic circuit 101 is stored inthe selected output FIFO.

The status information management portion 108 reads status informationof the unit circuit specified by the control portion 107 from the statusinformation storage portion 109 and supplies the status information tothe programmable logic circuit 101. Furthermore, the status informationmanagement portion 108 reads the status information of the unit circuitspecified by the control portion 107 from the programmable logic circuit101 and stores the status information into the status informationstorage portion 109.

The status information storage portion 109 stores status information109-1, 109-2, . . . , 109-N corresponding to the N unit circuits,respectively. The status information corresponding to the circuitinformation 103-k is hereinafter referred to as the status information109-k.

The operation time measuring portion 110 measures the operation time ofeach of the unit circuits and stores the measured operation times. Themeasured operation times can be referenced from the control portion 107.

The clock-and-voltage supply portion 111 supplies a clock signal and avoltage to the programmable logic circuit 101.

The control portion 107 monitors the amount of data held in the FIFOs106-1, 106-2, . . . , 106-(N−1), 106-a, and 106-b. The control portion107 selects the unit circuit realized by the programmable logic circuit101. The control portion 107 provides control when the unit circuitrealized by the programmable logic circuit 101 is switched. The controlportion 107 stores identifiers for the unit circuits operating in theprogrammable logic circuit 101.

The control portion 107 checks the operation time of each of the unitcircuits using the operation time measuring portion 110. The controlportion 107 estimates the voltage (operating voltage) supplied to theprogrammable logic circuit 101 and the frequency (clock frequency) ofthe supplied clock signal, using the operation times of the unitcircuits. The control portion 107 informs the clock-and-voltage supplyportion 111 of the estimated operating voltage and clock frequency.According to the notification, the clock-and-voltage supply portion 111modifies the operating voltage and clock frequency.

When a new unit circuit starts to operate under the unitcircuit-switching control provided by the programmable logic circuit101, the control portion 107 informs the operation time measuringportion 110 of the identifier of the unit circuit that has startedoperating. In response to the notification, the operation time measuringportion 110 measures the operation time of the unit circuit.

When the operation of the unit circuit is stopped under the unitcircuit-switching control provided by the programmable logic circuit101, the control portion 107 informs the operation time measuringportion 110 of the stoppage of the operation. In response to thenotification, the operation time measuring portion 110 stops themeasurement of the operation time of the unit circuit.

FIG. 4 is a flowchart illustrating processing of the control portion 107to find the clock frequency and operating voltage, using the operationtimes of the unit circuits. The processing of the control portion 107for finding the clock frequency and operating voltage is described belowwith reference to FIG. 4.

(Step 401)

The control portion 107 monitors the operation time of each unit circuitheld in the operation time measuring portion 110 per a given time. Inthe present exemplary embodiment, the control portion 107 monitors theoperation times per a given time. The time intervals of monitoring maybe variable. Furthermore, the control portion may monitor when someevent has occurred, for example, when the unit circuit realized by theprogrammable logic circuit 101 is switched.

(Step 402)

The control portion 107 estimates the amount of processing of each unitcircuit. In the present exemplary embodiment, the amount of processingis defined as the product of the operation time and clock frequency. Theamount of processing is not limited to the product of the operation timeand clock frequency. The product may be found using a functionreflecting the characteristics of the unit circuits or a conversiontable. Alternatively, the product may be found from the amount of inputdata and the amount of output data.

(Step 403)

The control portion 107 finds the clock frequency of the programmablelogic circuit 101, using the estimated amount of processing. In thepresent embodiment, the control portion 107 finds a clock frequencysufficient to perform a slightly larger amount of processing than thetotal of the estimated amounts of processing for the same time as thetime interval for which operation times are monitored. In the presentexemplary embodiment, the control portion 107 finds a clock frequencysufficient to perform 5% greater amount of processing than the total ofthe estimated amounts.

The control portion 107 first finds the sum of the amounts of processingof all the unit circuits. The control portion 107 finds an increasedamount of processing by multiplying the sum of amounts of processing by105%. In the present exemplary embodiment, the amount of processing isthe product of the clock frequency and the operation time and so thecontrol portion 107 finds a new clock frequency by dividing theincreased amount of processing by the monitor time interval.

In the present exemplary embodiment, the increased amount of processingis set to 5%. This value may be appropriately varied. Furthermore, thevalue may not be restricted to a fixed ratio. The range of increase maybe dynamically varied according to variation in the amount ofprocessing. In addition, the amount may not be determined by a ratio; afixed amount of processing may be added.

Alternatively, the sum of amounts of processing may be increased orreduced using another index such as the amounts of data stored in theFIFOs. A new clock frequency may be found by dividing the amount ofprocessing by the monitor time interval.

(Step 404)

The control portion 107 finds the operating voltage supplied to theprogrammable logic circuit 101 from the found clock frequency.Generally, the relation between the clock frequency and operatingvoltage depends on the kind or type of the programmable logic circuit101. Accordingly, the control portion 107 may find the voltage using afunction or conversion table created by referring to a table sheet orthe like.

(Step 405)

The control portion 107 informs the clock-and-voltage supply portion 111of the found operating voltage and clock frequency. Theclock-and-voltage supply portion 111 modifies the clock frequency andoperating voltage.

As described above, the logic circuit system of the present exemplaryembodiment can automatically vary the clock frequency and operatingvoltage according to the processing capability imposed on theprogrammable logic circuit and, therefore, the power consumption can bereduced.

Second Exemplary Embodiment of a Logic Circuit System

A logic circuit system of a second exemplary embodiment of the presentinvention is described below. The present exemplary embodiment differswith the first exemplary embodiment in the number of programmable logiccircuits. In the present exemplary embodiment, there are pluralprogrammable logic circuits. So the structure of a control portion 507is different from that of the control portion 107 of the first exemplaryembodiment. FIG. 5 shows the structure of the logic circuit system ofthe present exemplary embodiment.

The logic circuit system of the present exemplary embodiment can operateplural unit circuits at the same time. The control portion 507determines an assignment of unit circuits to programmable logic circuits101-1, 101-2, . . . , 101-m. Note that the initial values may bepredetermined.

Where there are plural programmable logic circuits, the control of theclock frequency and operating voltage as described in the firstexemplary embodiment may be provided for each individual programmablelogic circuit. However, where it is possible to reduce the operatingvoltages of all the programmable logic circuits at the same time, thereis the advantage that the number of components necessary to adjust theclock frequency and voltage can be reduced. In the present exemplaryembodiment, it is assumed that all programmable logic circuits operatewith the same frequency of clock signal and same operating voltage. Atechnique of adjusting the clock frequency and operating voltage in thiscase is described below.

FIG. 7 shows the configuration of the control portion 507 of the presentembodiment. The control portion 507 has a switching control portion 701for switching the unit circuit operated by each programmable logiccircuit, a circuit assignment table 702 storing the relation betweeneach programmable logic circuit and a unit circuit operated on theprogrammable logic circuit, and an assignment control portion 703 formodifying the assignment of the unit circuits to the programmable logiccircuits, the operating voltages of all the programmable logic circuits,and the clock frequency.

FIG. 6 illustrates the processing performed by the assignment controlportion 703. For purposes of explanation, FIG. 6 shows an example inwhich there are four programmable logic circuits, however, the presentinvention is not limited to this case. The assignment control portion703 reduces the surplus of the processing capability by adjusting theassignment of the unit circuits to the programmable logic circuits. Thisreduces the clock frequency and operating voltage and thus reduces thepower consumption.

A graph 600A indicates the processing capability imposed on eachprogrammable logic circuit prior to adjustment of the assignment of theunit circuits. A graph 600B indicates the processing capability imposedon each programmable logic circuit after the adjustment of theassignment of the unit circuits.

On the graph 600A, load is concentrated in the programmable logiccircuit A. The programmable logic circuit A requires high processingcapability. The operating voltage and clock frequency need to be setsuch that the programmable logic circuit A can have the requiredprocessing capability 601A. The operating voltage and clock frequencyare common to all the programmable logic circuits. As a result,programmable logic circuits B, C, and D also have high processingcapabilities.

However, the programmable logic circuits B, C, and D do not require ashigh processing capability as the logic circuit A. Especially, theprogrammable logic circuit D uses only half or below of the processingcapability. Therefore, on the graph 600A, the processing capability hasa large amount of surplus 602A.

Accordingly, in this example the assignment control portion 703 assignsprocessing 2 assigned to the programmable logic circuit A on which thehighest processing capability is imposed to the programmable logiccircuit D on which the lowest processing capability is imposed. Thegraph 600B indicates a graph obtained after the adjustment.

On the graph 600B, the processing capabilities imposed on theprogrammable logic circuits are almost flat or almost equivalent betweenthe programmable logic circuits. It is required that the operatingvoltage and clock frequency are set so that the programmable logiccircuit D can have the required processing capability 601B. Since therequired processing capability 601B is lower than the requiredprocessing capability 601A, the operating voltage and clock frequencycan be made lower than prior to the adjustment. The surplus 602B of theprocessing capability is lower than the surplus 602A of the processingcapability. As a whole, the operation can be performed at higherefficiency than prior to the adjustment.

The assignment control portion 703 stores the assignment of the unitcircuits made after adjustment into the circuit assignment table 702.The control portion 703 informs the clock-and-voltage supply portion 111of the estimated operating voltage and clock frequency.

The switching control portion 701 provides a unit circuit-switchingcontrol for switching the unit circuit operated in each programmablelogic circuit based on the assignment of the unit circuits stored in thecircuit assignment table 702.

FIG. 8 is a flowchart of processing for adjusting the assignment of unitcircuits performed by the assignment control portion 703. The processingof the assignment control portion 703 is described below with referenceto the figure.

(Step 801)

The assignment control portion 703 finds the total operation times ofthe programmable logic circuits. The control portion 703 checks theoperation times of the unit circuits, using the operation time measuringportion 110, and totals the operation times of the unit circuits foreach programmable logic circuit to find the total operation time of eachprogrammable logic circuit.

(Step 802)

The assignment control portion 703 finds maximum and minimum values ofthe total operation time and calculates the difference between them.

(Step 803)

The assignment control portion 703 compares the difference between themaximum and minimum values of the total operation time with a thresholdvalue. Where the difference is less than the threshold value, thecontrol portion 703 performs processing of step 805. Where the thresholdvalue is exceeded, the control portion performs processing of step 804.

(Step 804)

The assignment control portion 703 modifies the assignment of the unitcircuit. The control portion 703 assigns one of the unit circuitsassigned to the programmable logic circuit of a maximum total operationtime to the programmable logic circuit of a minimum total operationtime.

The assignment control portion 703 selects the one of the unit circuitshaving an operation time closest to a half of the difference between themaximum and minimum values of the total operation time. The method ofselecting a unit circuit is not limited to this scheme. The unit circuitmay be selected at random. Also, the unit circuit having the longestoperation time or shortest operation time may be selected. In addition,plural unit circuits may be selected.

(Step 805)

The assignment control portion 703 modifies the operating voltage andclock frequency of the programmable logic circuit 101. Where theassignment is modified, the assignment control portion 703 finds theclock frequency and operating voltage, using the maximum value of thetotal operation times of the programmable logic circuits after thereassignment. The clock frequency and operating voltage are found in thesame way as in the first exemplary embodiment.

Where the assignment is not modified, the clock frequency and operatingvoltage are found, using the maximum value of the present totaloperation times of the programmable logic circuits.

Where there are plural programmable logic circuits, the logic circuitsystem of the present exemplary embodiment can suppress the maximumvalue of the required processing capability by dispersing the processingamong the programmable logic circuits as described above.

Consequently, the clock frequency and operating voltage can beautomatically varied according to the processing capability imposed onthe whole system. Hence, the power consumption can be reduced.

Third Exemplary Embodiment of a Logic Circuit System

A logic circuit system of a third exemplary embodiment of the presentinvention is described below with reference to FIG. 9. The logic circuitsystem of the present exemplary embodiment is identical in configurationwith the second exemplary embodiment. The operation of the assignmentcontrol portion 703 is different.

FIG. 9 is a flowchart of processing performed by the assignment controlportion 703 of the present exemplary embodiment to adjust the assignmentof the unit circuits.

(Step 901)

The assignment control portion 703 finds the total operation time ofeach programmable logic circuit. The total operation time of eachprogrammable logic circuit is found by totalizing the operation times ofthe unit circuits for each programmable logic circuit.

(Step 902)

The assignment control portion 703 finds the average of the totaloperation times of all the programmable logic circuits.

(Step 903)

The assignment control portion 703 obtains the difference between thetotal operation time of each programmable logic circuit and the averagetotal operation time. The assignment control portion 703 subtracts theaverage total operation time from the total operation time. Therefore,where the total operation time is longer than the average totaloperation time, the difference is positive.

(Step 904)

The assignment control portion 703 compares the absolute difference witha threshold for each programmable logic circuit to find a programmablelogic circuit whose absolute difference exceeds the threshold. Theassignment control portion 703 performs processing of step 905 if thereis not any such programmable logic circuit. The control portion performsprocessing of step 906 if there is.

(Step 905)

The assignment control portion 703 finds the clock frequency andoperating voltage in the same way as the step 805 of the secondexemplary embodiment. Then, the assignment control portion 703 informsthe clock-and-voltage supply portion 111 of the found clock frequencyand operating voltage.

(Step 906)

Where there is any programmable logic circuit whose absolute differenceexceeds the threshold, the assignment control portion 703 modifies theassignment of the unit circuits. The assignment control portion 703assigns at least one unit circuit assigned to the programmable logiccircuit of a maximum operation time to the programmable logic circuit ofa minimum operation time in the same way as in the second exemplaryembodiment.

(Step 907)

The assignment control portion 703 estimates the total operation time ofeach programmable logic circuit after the reassignment.

(Step 908)

The assignment control portion 703 finds the difference between thetotal operation time of each programmable logic circuit and averagetotal operation time of in the same way as in step 903 after thereassignment. The control portion again performs the processing of step904.

In the above description, the number of repetitions of the loopincluding the steps 904, 906, 907, and 908 is not limited. Inalternative embodiments of the system, the number of repetitions may belimited, or a method of increasing the threshold used in step 904according to the number of repetitions may be used to prevent an endlessloop.

Furthermore, in step 906, the assignment control portion 703 may assignthe unit circuit assigned to the programmable logic circuit having totaloperation time longer than the average total operation time to theprogrammable logic circuit having total operation time shorter than theaverage total operation time. The programmable logic circuit havingtotal operation time longer or shorter than the average total operationtime may be selected at random. Also, the programmable logic circuithaving a total operation time different from the average total operationtime to the greatest extent (greatest or shortest) may be selected.Alternatively, plural programmable logic circuits each having thelongest total operation time may be selected, or programmable logiccircuits each having higher or lower total operation time than somereference value may be selected.

As described so far, the logic circuit system of the present exemplaryembodiment can suppress the maximum value of the required processingcapability in case there are plural programmable logic circuits, bydispersing the processing to the programmable logic circuits.

In consequence, the clock frequency and operating voltage can beautomatically varied according to the processing capability imposed onthe whole system. Hence, the power consumption can be reduced.

Fourth Exemplary Embodiment of a Logic Circuit System

A logic circuit system of a fourth exemplary embodiment of the presentinvention is described below with reference to FIG. 10. In the presentexemplary embodiment, it is assumed that the operation times of the unitcircuits should be close to assumed values under an ideal state. Wherethe balance between the operation times of the unit circuits is poor,the assignment of the unit circuits to the programmable logic circuitsis modified.

The logic circuit system of the present exemplary embodiment is similarin configuration to the second exemplary embodiment except that theassignment control portion 703 holds previously given, assumed values ofthe operation times of the unit circuits and that the assignment controlportion 703 operates differently from the second embodiment.

FIG. 10 is a flowchart of processing of the assignment control portion703 of the present exemplary embodiment to adjust the assignment of theunit circuits.

(Step 1001)

The assignment control portion 703 finds the operation time of each unitcircuit and the total operation time of each programmable logic circuit.

(Step 1002)

The assignment control portion 703 finds the sum of the absolutedifferences between the operation times of the unit circuits and theirrespective assumed values. This sum reflects the degree of balancebetween the operation times of the unit circuits. If the balance isgood, the sum of the absolute values of the differences approaches zero.The sum increases as the balance deteriorates.

(Step 1003)

The assignment control portion 703 compares the sum of the absolutedifferences with a threshold. Where the sum of the absolute differencesis greater than the threshold, the assignment control portion 703performs processing of step 1004. Where the sum of the absolute valuesof the differences is smaller than the threshold, the assignment controlportion 703 performs processing of step 1006.

(Step 1004)

The assignment control portion 703 modifies the assignment of the unitcircuits to the programmable logic circuits. The assignment controlportion 703 modifies the assignment target of the unit circuit havingthe greatest difference between the actual operation time and assumedvalue. The assignment control portion 703 changes this unit circuit tothe programmable logic circuit having the shortest total operation time.

Note that the unit circuit for which the assignment is modified is notlimited to one. Plural unit circuits are also possible. Furthermore, theassignment control portion 703 can select the assignment target of theunit circuits at random.

(Step 1005)

The assignment control portion 703 estimates the operation times of theprogrammable logic circuits after the reassignment, using the assumedvalues of the operation times of the unit circuits.

(Step 1006)

The assignment control portion 703 finds the clock frequency andoperating voltage in the same way as step 805 of the second exemplaryembodiment and informs the clock-and-voltage supply portion 111 of thefound values.

The sum of the absolute differences is used as an index indicating thedegree of balance between the operation times of the unit circuits. Thesum of the squared differences may also be used.

As described so far, the logic circuit system of the present exemplaryembodiment can automatically vary the clock frequency and operatingvoltage according to the processing capability imposed on the wholesystem while maintaining ideal operation times of the unit circuits.Consequently, the circuits can be operated at appropriate voltagescorresponding to the processing capabilities. Hence, the powerconsumption can be reduced.

Where there are plural programmable logic circuits, the logic circuitsystem of the present exemplary embodiment can suppress the maximumvalue of the required processing capability by dispersing the processingto the programmable logic circuits as described above.

This makes it possible to vary the clock frequency and operating voltageautomatically according to the processing capability imposed on thewhole system. Therefore, the power consumption can be reduced.

Furthermore, the aforementioned effect, e.g., decrease in the powerconsumption, can be obtained while keeping the balance between theoperation times of the unit circuits because the difference between theactual operation time and assumed time of each unit circuit is takeninto consideration.

Modified Exemplary Embodiments

The logic circuit systems of the exemplary embodiments described so farperform processing only with the programmable logic circuits 101. Logiccircuit systems of modifications of the various exemplary embodimentsmay also use dedicated circuits. In this case, such a logic circuitsystem treats a dedicated circuit also as a single unit circuit. Withthis logic circuit system, the clock frequency and operating voltage aremodified in the same way as in the exemplary embodiments described sofar.

The operation time measuring portions 110 of the logic circuit systemsof the exemplary embodiments described so far measure and store theoperation times of the unit circuits. The operation time measuringportions 110 of modifications of the exemplary embodiments may measurethe operation times within some unit time (e.g., the operation timewithin the last period of 3 seconds) instead of the operation timesthemselves. Alternatively, the operation time measuring portions 110 maymeasure the ratio of the operation time to a predetermined unit time.

The logic circuit system of the fourth exemplary embodiment has takeninto account the balance between the operation times of the unitcircuits. The logic circuit system of a modification of the fourthexemplary embodiment can also use the number of switching operations asan index indicating the balance. The logic circuit system of themodification may assign the corresponding unit circuit to anotherprogrammable logic circuit, in case, for example, the number ofswitching operations has exceeded a predetermined number.

Each of the logic circuit systems of the second through fourth exemplaryembodiments has a plurality of programmable logic circuits. The logiccircuit systems of modifications of these exemplary embodiments can alsobe applied to cases where one programmable logic circuit is partitionedinto plural blocks.

In the exemplary embodiments described so far, programmable logiccircuits are provided in which each unit block performs logiccalculations. Logic circuit systems of modifications of the variousexemplary embodiments may have programmable logic circuits of othertype. For example, a programmable logic circuit in which each unit blockis capable of arithmetic calculations and a programmable logic circuitin which each unit block is capable of performing simple processing insoftware may also be used.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. A power changing apparatus configured to change operating voltages ofplural programmable logic circuits when plural unit circuits areoperated in a time-sharing manner using the programmable logic circuits,each of the programmable logic circuits having a circuit configurationthat is reconfigurable during operation using each of circuitconfiguration data corresponding to each of the plural unit circuits,power changing apparatus comprising: an assigning unit configured toassign each of said plural unit circuits to each of said programmablelogic circuits; an operation time measurer configured to measureoperation times for each of said plural unit circuits; a firstcalculating unit configured to calculate first total operation times foreach of said plural programmable logic circuits, each of the first totaloperation times corresponding to a sum of said operation times for eachof said plural programmable logic circuits; an assignment changing unitconfigured to change air assignment of said plural unit circuits usingsaid first total operation times; a second calculating unit configuredto calculate second total operation times for each of said pluralprogrammable logic circuits, each of the second total operation timescorresponding to a sum of said operation times for each of said pluralprogrammable logic circuits according to the changed assignment; a clockunit configured to find a frequency of a clock signal supplied to saidplural programmable logic circuits using a maximum value of said secondtotal operation times; an operating voltage unit configured to findoperating voltages of said plural programmable logic circuits using saidclock frequency; and an operating voltage changer configured to changethe operating voltage of each of the programmable logic circuits and thefrequency of the clock signal to the found operating voltage and thefound frequency, respectively.
 2. The apparatus of claim 1, wherein theassignment changing unit is further configured to reassign one or moreof said plural unit circuits assigned to the programmable logic circuithaving a maximum value of the first total operation times to theprogrammable logic circuit having a minimum value of the first totaloperation times.
 3. The apparatus of claim 1 further comprising astorage unit configured to store assumed values for each of theoperation times of said plural unit circuits, wherein the assignmentchanging unit changes the assignment when an error between the operationtime of each unit circuit and the assumed value is greater than apredetermined threshold.
 4. The apparatus of claim 1, wherein theassignment changing unit is further configured to find a reference valuefor said first total operation times, and change in the assignment incase an error between one of said first total operation times and saidreference value is greater than a predetermined threshold.